Combustor shell air recirculation system in a gas turbine engine

ABSTRACT

A shell air recirculation system for use in a gas turbine engine includes one or more outlet ports located at a bottom wall section of an engine casing wall and one or more inlet ports located at a top wall section of the engine casing wall. The system further includes a piping system that provides fluid communication between the outlet port(s) and the inlet port(s), a blower for extracting air from a combustor shell through the outlet port(s) and for conveying the extracted air to the inlet port(s), and a valve system for selectively allowing and preventing air from passing through the piping system. The system operates during less than full load operation of the engine to circulate air within the combustor shell but is not operational during full load operation of the engine.

FIELD OF THE INVENTION

The present invention relates to a combustor shell air recirculationsystem in a gas turbine engine, wherein the recirculation system isoperable during less than full load operation to create a more uniformair temperature distribution within the combustor shell.

BACKGROUND OF THE INVENTION

During operation of a gas turbine engine, air is pressurized in acompressor section then mixed with fuel and burned in a combustionsection to generate hot combustion gases. In a can annular gas turbineengine, the combustion section comprises an annular array of combustorapparatuses, sometimes referred to as “cans” or “combustors”, which eachsupply hot combustion gases to a turbine section of the engine where thehot combustion gases are expanded to extract energy therefrom to provideoutput power, which is in turn used to produce electricity.

SUMMARY OF THE INVENTION

In accordance with the present invention, a gas turbine engine isprovided including a longitudinal axis defining an axial direction ofthe engine. The engine comprises a compressor section where air pulledinto the engine is compressed, a combustion section comprising aplurality of combustor apparatuses where fuel is mixed with at least aportion of the compressed air from the compressor section and burned tocreate hot combustion gases, and a turbine section where the hotcombustion gases from the combustion section are expanded to extractenergy therefrom. The engine further comprises a casing having a portiondisposed about the combustion section, the casing portion comprising acasing wall having a top wall section defining a top dead center, leftand right side wall sections, and a bottom wall section defining abottom dead center. The casing portion further defines an interiorvolume in which the combustor apparatuses and air compressed by thecompressor section are located. The engine additionally comprises ashell air recirculation system.

According to a first aspect of the present invention, the shell airrecirculation system comprises at least one outlet port located at thebottom wall section of the casing wall and first and second inlet portslocated at the top wall section of the casing wall. The inlet ports arecircumferentially spaced apart from one another and are located atgenerally the same axial location. The shell air recirculation systemfurther comprises a piping system that provides fluid communicationbetween the at least one outlet port and the inlet ports, a blower forextracting air from the interior volume of the casing portion throughthe at least one outlet port and for conveying the extracted air to theinlet ports, and a valve system for selectively allowing and preventingair from passing through the piping system. During a first mode ofengine operation, at least some of the air in the interior volume of thecasing portion is introduced into the combustor apparatuses for beingburned with fuel to create hot combustion gases, and the valve systemsubstantially prevents air from passing through the piping system.During a second mode of engine operation, the valve system allows air topass through the piping system such that at least a portion of the airin the interior volume of the casing portion is extracted from the atleast one outlet port by the blower and conveyed by the blower to theinlet ports for injection into the top wall section of the casing wall.

According to a second aspect of the present invention, the shell airrecirculation system comprises at least one outlet port located at thebottom wall section of the casing wall and at least one inlet portlocated at the top wall section of the casing wall. The shell airrecirculation system further comprises a piping system that providesfluid communication between the at least one outlet port and the atleast one inlet port, a blower for extracting air from the interiorvolume of the casing portion through the at least one outlet port andfor conveying the extracted air to the at least one inlet port, and avalve system for selectively allowing and preventing air from passingthrough the piping system. During a first mode of engine operation, atleast some of the air in the interior volume of the casing portion isintroduced into the combustor apparatuses for being burned with fuel tocreate hot combustion gases, and the valve system substantially preventsair from passing through the piping system. During a second mode ofengine operation, the valve system allows air to pass through the pipingsystem such that at least a portion of the air in the interior volume ofthe casing portion is extracted from the at least one outlet port by theblower and conveyed by the blower to the at least one inlet port. The atleast one inlet port is configured such that the air injected therebyflows from the top wall section of the casing wall down the left andright side wall sections of the casing wall toward the bottom wallsection of the casing wall.

According to a third aspect of the present invention, the combustionsection comprises a can annular combustion section comprising an annulararray of combustor apparatuses. The shell air recirculation systemaccording to this embodiment comprises at least one outlet port locatedat the bottom wall section of the casing wall and at least one inletport located at the top wall section of the casing wall. At least one ofthe outlet and inlet ports also functions as a steam augmentation pipeto introduce high pressure steam into the interior volume of the casingportion during a first mode of operation. The shell air recirculationsystem further comprises a piping system that provides fluidcommunication between the at least one outlet port and the at least oneinlet port, a blower for extracting air from the interior volume of thecasing portion through the at least one outlet port and for conveyingthe extracted air to the at least one inlet port, and a valve system forselectively allowing and preventing air from passing through the pipingsystem. During the first mode of engine operation, at least some of theair in the interior volume of the casing portion is introduced into thecombustor apparatuses for being burned with fuel to create hotcombustion gases, and the valve system substantially prevents air frompassing through the piping system. During a second mode of engineoperation, the valve system allows air to pass through the piping systemsuch that at least a portion of the air in the interior volume of thecasing portion is extracted from the at least one outlet port by theblower and conveyed by the blower to the at least one inlet port forinjection into the top section of the casing wall.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the present invention, it is believed that thepresent invention will be better understood from the followingdescription in conjunction with the accompanying Drawing Figures, inwhich like reference numerals identify like elements, and wherein:

FIG. 1 is a side view, partially in section, of a gas turbine engineincluding a combustor shell air recirculation system according to anembodiment of the invention;

FIG. 2 is a schematic illustration of the combustor shell airrecirculation system illustrated in FIG. 1; and

FIG. 3 is a sectional view of a portion of a combustor shell airrecirculation system according to another aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration, and not by way oflimitation, specific preferred embodiments in which the invention may bepracticed. It is to be understood that other embodiments may be utilizedand that changes may be made without departing from the spirit and scopeof the present invention.

Referring to FIG. 1, a gas turbine engine 10 constructed in accordancewith the present invention is shown. The engine 10 includes a compressorsection 12, a combustion section 14 including a plurality of combustors16, also referred to herein as “combustor apparatuses,” and a turbinesection 18. It is noted that only one combustor 16 is illustrated inFIG. 1 for clarity, but the engine 10 according to the present inventionpreferably comprises an annular array of combustors 16 that are disposedabout a longitudinal axis L_(A) of the engine 10 that defines an axialdirection within the engine 10. Such a configuration is typicallyreferred to as a “can-annular combustion system”.

The compressor section 12 inducts and pressurizes inlet air, at least aportion of which is directed to a combustor shell 20 for delivery to thecombustors 16. The air in the combustor shell 20 is hereinafter referredto as “shell air”. Other portions of the pressured air may be extractedfrom the combustion section 12 to cool various components within theengine 10.

Upon entering the combustors 16, the compressed air from the compressorsection 12 is mixed with fuel and ignited to produce high temperaturecombustion gases flowing in a turbulent manner and at a high velocitywithin the respective combustor 16. The combustion gases in eachcombustor 16 then flow through a respective transition duct 22 to theturbine section 18 where the combustion gases are expanded to extractenergy therefrom. The energy extracted from the combustion gases is usedprovide rotation of a turbine rotor 24, which extends parallel to arotatable shaft 26 that extends axially through the engine 10.

As shown in FIG. 1, an engine casing 30 is provided to enclose therespective engine sections 12, 14, 18. A portion 30A of the casing 30disposed about combustion section 14 comprises a casing wall 32 thatdefines the combustor shell 20, i.e., the combustor shell 20 defines aninterior volume within the casing portion 30A. Referring to FIG. 2, thecasing wall 32 includes a top wall section 32A, left and right side wallsections 32B, 32C, and a bottom wall section 32D. The top wall section32A defines a top dead center 34 of the casing wall 32, which comprisesan uppermost area of the casing portion 30A, and the bottom wall section32D defines a bottom dead center 36 of the casing wall 32, whichcomprises a lowermost area of the casing portion 30A.

A shell air recirculation system 40 according to an aspect of thepresent invention will now be described. Referring to FIG. 2, the shellair recirculation system 40 in the embodiment shown comprises first andsecond outlet ports 42A, 42B located at the bottom wall section 32D ofthe casing wall 32. While the shell air recirculation system 40according to this embodiment comprises first and second outlet ports42A, 42B, any suitable number of outlet ports can be provided, includinga single outlet port.

As shown in FIG. 2, the outlet ports 42A, 42B are circumferentiallyspaced apart and are located at generally the same axial location,wherein the bottom dead center 36 of the casing wall 32 is locatedbetween the outlet ports 42A, 42B. According to one aspect of theinvention, at least one of the outlet ports 42A, 42B may also functionas a steam augmentation pipe to channel high pressure steam into thecombustor shell 20 to effect an increase in output power of the engine10, i.e., by effecting higher combustion gas flow rates through turbinesection 18.

The shell air recirculation system 40 further comprises a piping system44 that is provided to convey shell air that is extracted from thecombustor shell 20 through the outlet ports 42A, 42B to first and secondinlet ports 46A, 46B, which are located at the top wall section 32A ofthe casing wall 32. While the shell air recirculation system 40according to this embodiment comprises first and second inlet ports 46A,46B, any suitable number of inlet ports can be provided, including asingle inlet port.

As shown in FIG. 2, the inlet ports 46A, 46B are circumferentiallyspaced apart and are located at generally the same axial location,wherein the first inlet port 46A is located near the left side wallsection 32B of the casing wall 32 and the second inlet port 46B islocated near the right side wall section 32C of the casing wall 32.According to one aspect of the invention, at least one of the inletports 46A, 46B may also function as a steam augmentation pipe to channeladditional high pressure steam into the combustor shell 20.

The shell air recirculation system 40 still further comprises a valvesystem 48 comprising first and second valves 48A, 48B in the embodimentshown, and a blower 50. The valve system 48 and the blower 50 arecontrolled by a controller 52 to selectively allow or prevent shell airfrom passing through the piping system 44 from the outlet ports 42A, 42Bto the inlet ports 46A, 46B, as will be described in detail below. Theblower 50 is provided for extracting the shell air from the combustorshell 20 through the outlet ports 42A, 42B and for conveying theextracted shell air to the inlet ports 46A, 46B when the valve system 48is open.

A method for utilizing the shell air recirculation system 40 will now bedescribed. During normal operation of the engine 10, also known as fullload or base load operation and also referred to herein as a first modeof engine operation, the first and second valves 48A, 48B are closed andthe blower 50 is turned off or is otherwise not operational. Hence, thevalve system 48 substantially prevents shell air from passing throughthe piping system 44. At least a portion of the shell air is providedinto the combustors 16 to be burned with fuel as discussed above.Additional portions of the shell air may be used to cool variouscomponents within the engine 10, as will be apparent to those havingskill in the art.

Upon initiation of a turn down operation, which is implemented totransition the engine 10 to a shut down state or a turning gear state,fuel and shell air supplied to the combustors 16 is gradually ceased,such that the production of high temperature combustion gases in thecombustors 16 is gradually decreased to null upon the engine 10 beingtransitioned to the shut down state or the turning gear state. Oncecombustion gases are no longer produced in the combustors 16, rotationof the turbine rotor 24 is not able to be effected by combustion gases.In such a situation, slow rotation of the turbine rotor 24 may beeffected by an outside power supply (not shown), such as by a start-upmotor, in an operating state referred to herein as a turning gear state.Alternatively, rotation of the turbine rotor 24 may be completelystopped in an operating state referred to herein as a shut down state.In a typical engine 10, such a turn down operation may take at leastabout 10-15 minutes to completely transition the engine 10 to a turninggear state, during which time combustion of a gradually decreasing levelcontinues in the combustors 16 to produce high temperature combustiongases, which gases are conveyed into the turbine section 18 to providerotation of the turbine rotor 24. The second mode of engine operation,as used herein, is meant to encompass turn down operation, a turninggear state, or a shut down state of the engine 10.

According to an aspect of the present invention, upon the initiation ofa turn down operation to transition the engine 10 to either a turninggear state or a shut down state, the controller 52 opens the first andsecond valves 48A, 48B such that the valve system 48 allows air to passthrough the piping system 44. The blower 50 is turned on by thecontroller 52 during the second mode of operation to extract shell airfrom the bottom wall section 32D of the casing wall 32 through theoutlet ports 42A, 42B. The blower 50 conveys, i.e., pumps, the extractedshell air through the piping system 44 such that the extracted shell airis injected into the top wall section 32A of the casing wall 32 throughthe inlet ports 46A, 46B.

According to another aspect of the invention, the turn down operationmay be implemented to transition the engine 10 from full load operationto a turning gear state, which may be run for a predetermined time oruntil one or more select engine components reaches a predefinedtemperature, at which point the engine 10 may be transitioned to a shutdown state. Under this arrangement, during the turning gear state, thevalves 48A, 48B are maintained in open positions and operation of theblower 50 is continued to extract shell air from the bottom wall section32D of the casing wall 32 through the outlet ports 42A, 42B, to conveythe extracted shell air through the piping system 44, and to inject theextracted shell air into the top wall section 32A of the casing wall 32through the inlet ports 46A, 46B. However, upon the engine 10 enteringthe shut down state, i.e., after completion of the turning gear state,the blower 50 may be turned off or otherwise disabled to stop thepumping of shell air through the piping system 44. During the shut downstate, the valves 48A, 48B may remain opened or the controller 52 mayclose them, but they would be closed by the controller 52 upon theinitiation of an engine start up procedure.

As shown in FIG. 2, the air injected by the inlet ports 46A, 46B intothe combustor shell 20 flows from the top wall section 32A of the casingwall 32 down the respective left and right side wall sections 32B, 32Ctoward the bottom wall section 32D. The shell air recirculation system40 thus functions to circulate the shell air within the combustor shell20 during less than full load operation so as to create a more uniformshell air temperature distribution within the combustor shell 20.Otherwise, hotter shell air would tend to migrate to the top wallsection 32A, thus resulting in hotter temperatures at the top wallsection 32A than at the bottom wall section 32D. Further, the shell airtoward the bottom wall section 32D that is extracted through the outletports 42A, 42B by the blower 50 and injected through the inlet ports46A, 46B is generally cooler than the shell air toward the top wallsection 32A, thus resulting in an even more uniform shell airtemperature distribution within the combustor shell 20.

The more uniform shell air temperature distribution within the combustorshell 20 effected by the shell air recirculation system 40 is believedto reduce or prevent issues that might result from components within andaround the combustor shell 20 thermally growing at different rates, suchas distortion of the engine casing 30 and/or rubbing of turbine bladetips T_(T) in the turbine section 18 against the casing 30, thuslengthening a lifespan of these components and maintaining a tight bladetip clearance during full load operation for improved turbineefficiency. It is noted that since the shell air recirculation system 40according to the present invention injects only shell air into thecombustor shell 20, which shell air is extracted from the bottom wallsection 32D through the outlet ports 42A, 42B by the blower 50, the costand complexity of the shell air recirculation system 40 is reduced,i.e., compared to a system that uses structure such as an ejector toinject highly pressurized air into the combustor shell 20.

As noted above, one or more of the outlet and inlet ports 42A, 42B, 46A,46B may also function as steam augmentation pipes to channel highpressure steam into the combustor shell 20 to effect an increase inoutput power of the engine 10. Such steam introduction is typically onlyperformed during full load operation. If any of the outlet and inletports 42A, 42B, 46A, 46B also function as steam augmentation pipes,these ports 42A, 42B, 46A, 46B preferably extend straight into thecasing wall 32 and terminate a short distance into the combustor shell20, as shown in FIGS. 1 and 2. Using the outlet and inlet ports 42A,42B, 46A, 46B as steam augmentation pipes may be especially advantageousif the shell air recirculation system 40 is implemented in an existingengine 10, i.e., in a retrofit design, as additional pipes that extendthrough the casing wall 32 would not be required, thus reducing thecomplexity of installing the shell air recirculation system 40 in anexisting engine 10.

If the outlet and inlet ports 42A, 42B, 46A, 46B are not to function assteam augmentation pipes, one or more of these ports 42A, 42B, 46A, 46Bcould have specially configured tips to modify shell air extractionand/or injection from and/or into the combustor shell 20. For example,referring to FIG. 3, a shell air recirculation system 140 constructed inaccordance with another embodiment of the invention is shown, whereinstructure similar to that described above with reference to FIGS. 1 and2 includes the same reference number increased by 100. Further, onlystructure that differs from the embodiment discussed above withreference to FIGS. 1 and 2 will be discussed herein for FIG. 3. As apoint of reference, the view of the shell air recirculation system 140shown in FIG. 3 is taken along line 3-3 illustrated in FIG. 1, andselect engine 110 and shell air recirculation system 140 components havebeen removed from FIG. 3 for clarity.

In this embodiment, the outlet ports 142A, 142B have conical shaped tips142A₁, 142B₁ to increase the amount of shell air that can be extractedthereby.

Further, the inlet ports 146A, 146B according to this embodiment havetips 146A₁, 146B₁ that are angled circumferentially toward one anotherand are also angled axially in a direction toward the compressor section(not shown in this embodiment) and away from the turbine section (notshown in this embodiment). The inlet ports 146A, 146B according to thisembodiment are thus configured such that they inject shell air at leastpartially in the circumferential direction toward one another and towardthe top dead center 134 of the casing wall 132, which is locatedcircumferentially between the first and second inlet ports 146A, 146B asshown in FIG. 3, i.e., the shell air injected by the inlet ports 146A,146B includes a circumferential velocity component.

After flowing to the top dead center 134 of the casing wall 132, the airinjected by the inlet ports 146A, 146B flows from the top wall section132A of the casing wall 132 down the respective left and right side wallsections 132B, 132C toward the bottom wall section 132D. Since the airinjected by the inlet ports 146A, 146B according to this embodimentflows to the top dead center 134 of the casing wall 132, it is believedto be ensured that the shell air at the top dead center 134 of thecasing wall 132, which may be the hottest shell air within the combustorshell 120, is circulated with the remaining shell air. Further, sincethe shell air injected by the inlet ports 146A, 146B according to thisembodiment also flows in the axial direction toward the compressorsection of the engine 110, i.e., the shell air injected by the inletports 146A, 146B includes an axial velocity component, it is believed tobe ensured that a greater amount of the shell air within the combustorshell 120 is circulated.

It is noted that the outlet and inlet ports described herein could belocated at other axial locations within the casing portion than thelocations shown in FIGS. 1-3. Further, multiple rows of outlet and inletports may be utilized to further improve shell air circulation withinthe combustor shell.

It is also noted that if only a single inlet port is used, i.e., asopposed to using first and second inlet ports in the embodimentsdiscussed above, the single inlet port could be configured to inject airdown both the left and right side wall sections of the casing wall.Examples of such an inlet port include a dual tipped inlet port, whereina first tip is directed to the left side wall section and a second tipis directed to the right side wall section, or the inlet port could havelouvers or fins that are provide to inject air in the desireddirections. Further, such a single inlet port could be located at thetop dead center of the casing wall to provide a more efficient aircirculation within the combustor shell. Moreover, such a single inletport could also be configured such that the shell air injected therebyincludes an axial velocity component.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention.

It is therefore intended to cover in the appended claims all suchchanges and modifications that are within the scope of this invention.

What is claimed is:
 1. A gas turbine engine including a longitudinalaxis defining an axial direction of the engine, the engine comprising: acompressor section where air pulled into the engine is compressed; acombustion section comprising a plurality of combustor apparatuses wherefuel is mixed with at least a portion of the compressed air from thecompressor section and burned to create hot combustion gases; a turbinesection where the hot combustion gases from the combustion section areexpanded to extract energy from the combustion gases; a casing having aportion disposed about the combustion section, the casing portioncomprising a casing wall having a top wall section defining a top deadcenter, left and right side wall sections, and a bottom wall sectiondefining a bottom dead center, the casing portion further defining aninterior volume in which the combustor apparatuses and air compressed bythe compressor section are located; and a shell air recirculation systemcomprising: at least one outlet port located at the bottom wall sectionof the casing wall; first and second inlet ports located at the top wallsection of the casing wall, the inlet ports being circumferentiallyspaced apart from one another and located at generally the same axiallocation; a piping system that provides fluid communication between theat least one outlet port and the inlet ports; a blower for extractingair from the interior volume of the casing portion through the at leastone outlet port and for conveying the extracted air to the inlet ports;and a valve system for selectively allowing and preventing air frompassing through the piping system; wherein: during a first mode ofengine operation: at least some of the air in the interior volume of thecasing portion is introduced into the combustor apparatuses for beingburned with fuel to create hot combustion gases; and the valve systemsubstantially prevents air from passing through the piping system; andduring a second mode of engine operation, the valve system allows air topass through the piping system such that at least a portion of the airin the interior volume of the casing portion is extracted from the atleast one outlet port by the blower and conveyed by the blower to theinlet ports for injection into the top wall section of the casing wall.2. The gas turbine engine of claim 1, wherein the first mode of engineoperation is full load operation.
 3. The gas turbine engine of claim 2,wherein the second mode of engine operation is less than full loadoperation.
 4. The gas turbine engine of claim 1, wherein the inlet portsare configured such that the air injected thereby includes a velocitycomponent in the circumferential direction.
 5. The gas turbine engine ofclaim 4, wherein the inlet ports are configured such that they injectair at least partially in directions toward one another and toward thetop dead center of the casing wall, which is located circumferentiallybetween the inlet ports.
 6. The gas turbine engine of claim 5, whereinthe inlet ports are configured such that the air injected thereby flowsfrom the top wall section of the casing wall down the left and rightside wall sections of the casing wall toward the bottom wall section ofthe casing wall.
 7. The gas turbine engine of claim 6, wherein the inletports are configured such that the air injected thereby includes avelocity component in the axial direction.
 8. The gas turbine engine ofclaim 1, wherein the at least one outlet port and the inlet ports alsofunction as steam augmentation pipes to introduce high pressure steaminto the interior volume of the casing portion during the first mode ofoperation.
 9. The gas turbine engine of claim 1, wherein the combustionsection comprises a can annular combustion section and the plurality ofcombustor apparatuses comprises an annular array of combustorapparatuses.
 10. A gas turbine engine including a longitudinal axisdefining an axial direction of the engine, the engine comprising: acompressor section where air pulled into the engine is compressed; acombustion section comprising a plurality of combustor apparatuses wherefuel is mixed with at least a portion of the compressed air from thecompressor section and burned to create hot combustion gases; a turbinesection where the hot combustion gases from the combustion section areexpanded to extract energy from the combustion gases; a casing having aportion disposed about the combustion section, the casing portioncomprising a casing wall having a top wall section defining a top deadcenter, left and right side wall sections, and a bottom wall sectiondefining a bottom dead center, the casing portion further defining aninterior volume in which the combustor apparatuses and air compressed bythe compressor section are located; and a shell air recirculation systemcomprising: at least one outlet port located at the bottom wall sectionof the casing wall; at least one inlet port located at the top wallsection of the casing wall; a piping system that provides fluidcommunication between the at least one outlet port and the at least oneinlet port; a blower for extracting air from the interior volume of thecasing portion through the at least one outlet port and for conveyingthe extracted air to the at least one inlet port; and a valve system forselectively allowing and preventing air from passing through the pipingsystem; wherein: during a first mode of engine operation: at least someof the air in the interior volume of the casing portion is introducedinto the combustor apparatuses for being burned with fuel to create hotcombustion gases; and the valve system substantially prevents air frompassing through the piping system; and during a second mode of engineoperation, the valve system allows air to pass through the piping systemsuch that at least a portion of the air in the interior volume of thecasing portion is extracted from the at least one outlet port by theblower and conveyed by the blower to the at least one inlet port,wherein the at least one inlet port is configured such that the airinjected thereby flows from the top wall section of the casing wall downthe left and right side wall sections of the casing wall toward thebottom wall section of the casing wall.
 11. The gas turbine engine ofclaim 10, wherein the first mode of engine operation is full loadoperation and the second mode of engine operation is less than full loadoperation.
 12. The gas turbine engine of claim 10, wherein the at leastone inlet port comprises first and second circumferentially spaced apartinlet ports located at generally the same axial location, wherein theinlet ports both inject air in a direction toward one another and towardthe top dead center of the casing wall.
 13. The gas turbine engine ofclaim 12, wherein the inlet ports are configured such that the airinjected thereby includes a velocity component in the axial directiontoward the compressor section and away from the turbine section.
 14. Thegas turbine engine of claim 10, wherein the at least one outlet port andthe at least one inlet port also function as steam augmentation pipes tointroduce high pressure steam into the interior volume of the casingportion during the first mode of operation.
 15. The gas turbine engineof claim 11, wherein the combustion section comprises a can annularcombustion section and the plurality of combustor apparatuses comprisesan annular array of combustor apparatuses.
 16. A gas turbine engineincluding a longitudinal axis defining an axial direction of the engine,the engine comprising: a compressor section where air pulled into theengine is compressed; a can annular combustion section comprising anannular array of combustor apparatuses where fuel is mixed with at leasta portion of the compressed air from the compressor section and burnedto create hot combustion gases; a turbine section where the hotcombustion gases from the combustion section are expanded to extractenergy from the combustion gases; a casing having a portion disposedabout the combustion section, the casing portion comprising a casingwall having a top wall section defining a top dead center, left andright side wall sections, and a bottom wall section defining a bottomdead center, the casing portion further defining an interior volume inwhich the combustor apparatuses and air compressed by the compressorsection are located; and a shell air recirculation system comprising: atleast one outlet port located at the bottom wall section of the casingwall; at least one inlet port located at the top wall section of thecasing wall, at least one of the outlet and inlet ports also functioningas a steam augmentation pipe to introduce high pressure steam into theinterior volume of the casing portion during a first mode of operation;a piping system that provides fluid communication between the at leastone outlet port and the at least one inlet port; a blower for extractingair from the interior volume of the casing portion through the at leastone outlet port and for conveying the extracted air to the at least oneinlet port; and a valve system for selectively allowing and preventingair from passing through the piping system; wherein: during the firstmode of engine operation: at least some of the air in the interiorvolume of the casing portion is introduced into the combustorapparatuses for being burned with fuel to create hot combustion gases;and the valve system substantially prevents air from passing through thepiping system; and during a second mode of engine operation, the valvesystem allows air to pass through the piping system such that at least aportion of the air in the interior volume of the casing portion isextracted from the at least one outlet port by the blower and conveyedby the blower to the at least one inlet port for injection into the topsection of the casing wall.
 17. The gas turbine engine of claim 16,wherein each of the outlet and inlet ports also functions as a steamaugmentation pipe to introduce high pressure steam into the interiorvolume of the casing portion during the first mode of operation.
 18. Thegas turbine engine of claim 16, wherein the at least one inlet portcomprises first and second circumferentially spaced apart inlet portslocated at generally the same axial location, wherein the first inletport is located near the left side wall section of the casing wall andthe second inlet port is located near the right side wall section of thecasing wall.
 19. The gas turbine engine of claim 18, wherein the inletports are configured such that the air injected thereby flows from thetop wall section of the casing wall down the respective left and rightside wall sections of the casing wall toward the bottom wall section ofthe casing wall.
 20. The gas turbine engine of claim 19, wherein theinlet ports are configured such that the air injected thereby includes avelocity component in the axial direction.